The present disclosure relates to a gas turbine engine having an improved noise signature.
Gas turbine engines are typically optimized to provide high efficiency, because this generally results in lower fuel burn, and thus lower running costs. However, the noise generated by a gas turbine engine used to power an aircraft is an important factor due to the impact that aircraft noise can have on communities.
In this regard, gas turbine engines generate a significant proportion of the noise produced by an aircraft. Regulations define an “Effective Perceived Noise Level” (EPNL) which is a measure of the impact of the generated noise as perceived by the human ear, taking into account factors such as frequency, absolute level, tonal components and duration of the noise.
A turbofan gas turbine engine comprises a number of different noise sources. For example, the fan itself is a source of noise, and that fan noise can be separated into two distinct components: a component that emanates in a forwards direction from the front of the engine; and a component that emanates in a rearward direction from the rear of the engine. Further noise sources include (but are not limited to) noise from the jet stream exhausted from the engine, noise from the turbine at the rear of the engine, and noise from the installation of the engine on the aircraft.